This invention is in the field of surgical devices, and more particularly relates to rigid fixation devices used to fuse bone structures in badly diseased or deformed ankle joints.
Some patients suffer from various problems which require at least a portion of an ankle joint to be effectively immobilized. This is usually done by inserting one or more rigid rods or pins (typically made of stainless steel and having a diameter roughly the size of a patient""s finger) into one or more bones in the ankle, and in the xe2x80x9chindfootxe2x80x9d portion of the foot (i.e., the portion of the foot which includes the heel). This will permanently affix certain bones to other bones. The medical term for this type of permanent bone fixation is xe2x80x9carthrodesisxe2x80x9d.
As used herein, the terms xe2x80x9crodxe2x80x9d, xe2x80x9cpinxe2x80x9d, and xe2x80x9cnailxe2x80x9d are used interchangeably. All three terms refer to a rigid component that is inserted into one or more bones, for the purpose of anchoring, stabilizing, repairing, or supporting the bone(s). Since this invention is limited to devices inserted into an ankle or foot, for the purpose of ankle arthrodesis, any references herein to rod, pin, or screw are limited to devices inserted into a calcaneal and/or tibial bone.
These components are also sometimes referred to as xe2x80x9cintramedullaryxe2x80x9d rods or pins; this term indicates that the rod/pin is inserted into the relatively soft center portion of a bone.
The term xe2x80x9crodxe2x80x9d usually implies a relatively large device, while the term xe2x80x9cpinxe2x80x9d implies a somewhat smaller device; however, there is no clear boundary between these terms.
As used herein, the term xe2x80x9cnon-threadedxe2x80x9d indicates that a rod or pin does not have screw-type threads on its external surface; however, a non-threaded rod or pin can have one or more threaded holes passing through it, for fixation screws, so long as the threads are not exposed on the external surface.
It should also be noted that, while the terms xe2x80x9crodxe2x80x9d, xe2x80x9cpinxe2x80x9d, or xe2x80x9cnailxe2x80x9d normally tend to imply that an implant does not have an externally threaded surface, some people and some documents do not adhere to that convention, and some implanted rods, pins, or nails have external threads (including, in some cases, threads that are shallow and are not used to generate thrust or compression as the device is rotated). Accordingly, even though the vertical rods that have been used to date as disclosed herein have not had external threads, such rods can be provided with one or more externally threaded regions if desired, and would still fall within the term xe2x80x9crodxe2x80x9d as used herein.
While the type of surgical procedure mentioned above severely limits flexibility and mobility within the ankle joint, it sometimes becomes necessary as a treatment for a condition such as severe arthritis, infection and/or avascular necrosis of one or more bones in the region, congenital deformity of the tibio-talar or talocalcaneal joint, or certain types of neuropathy. In all of those conditions, any motion of the bones relative to each other can cause severe pain in the foot or ankle, to a point where a patient becomes effectively unable to walk or put any pressure on that foot. Accordingly, immobilization of the ankle joint becomes an acceptable price to pay, if the patient can begin to walk again without excruciating pain in the ankle and foot.
Ankle arthrodesis has a long history, and began at least as early as the 1880""s (Albert 1882). In the early 1900""s, various efforts were made to use long slender bones from corpses (such as the fibula bone), in an attempt to affix various ankle components (e.g., Lexer 1906 and Albee 1915). By the 1960""s, intramedullary nailing had advanced to a point of using guide wires to properly locate steel pins, but these approaches tended to suffer from high infection rates. Other authors reported the use of Steinmann pins with external fixation (e.g., Russotti et al 1988), and transfibular pins and cannulated screws (e.g., Pappa et al 1992).
Subsequently, a two-component rod-and-pin structure was developed, with a vertical rod and a horizontal pin that are rigidly affixed to each other, at an angle which is essentially perpendicular, or obtuse (as explained below). This assembly is described and illustrated in articles such as Quill 1999. Since it is the closest known item of relevant prior art, it is also illustrated in FIG. 1, which is a lateral view of the inside surface of a right foot.
The vertical rod is inserted into a hole that is drilled into the bottom of the calcaneum (also called the heel bone, the calcaneal bone, and the os calcis). In patients having a normal or near-normal bone structure, this rod then passes through the talus (also called the talar bone; also called the ankle bone, by laymen), which sits directly on top of the calcaneum, as shown in FIG. 1. Regardless, the vertical rod of the two-pin assembly is driven into the center (marrow) portion of the tibia (the long bone which passes from the knee to the ankle; also called the shinbone by laymen). This vertical rod thereby permanently fuses the calcaneum (heel bone) to the tibia, and immobilizes that portion of the ankle joint. If this type of vertical pin is used by itself, this type of fixation would be called xe2x80x9ctibio-calcaneal arthrodesisxe2x80x9d.
In the second stage of the surgical operation used to emplace the two-pin device of the prior art, the smaller pin is inserted, in a roughly horizontal manner, through a hole drilled into the posterior (rear) face of the calcaneum. It passes through a hole in the vertical rod, and is driven close to the anterior tip of the calcaneal bone. Even though this pin is not strictly horizontal, it is referred to herein as the horizontal pin, to clearly distinguish it from the vertical rod, which is significantly larger and which is emplaced first.
As shown in pictures such as FIG. 1D in Quill 1999 (and in FIG. 1 herein), the anterior tip (i.e., the end that is closer to the patient""s toes) of the horizontal pin is slightly lower than the posterior tip (i.e., the end closest to the patient""s heel). This establishes an obtuse angle between the rod and the pin, designated as angle xcex1PA in FIG. 1. The roughly horizontal pin (assuming the patient""s foot is standing on a horizontal surface) is referred to herein as having a slightly xe2x80x9cdownwardxe2x80x9d angle, since the pin is driven forward into the foot from the entry point at the heel.
After both the rod and the pin have been properly emplaced in the patient""s foot, they are permanently affixed to the tibial and calcaneal bones, using threaded screws.
Two issues involving bone structures and terminology should be clarified. First, in a normal ankle joint, because of the placement of the bones, a straight rod which passes vertically through the calcaneum (the heel bone) and into the tibia (in the shin) will normally pass through the talus (the ankle bone). Accordingly, a reference to xe2x80x9ctibio-calcaneal arthrodesisxe2x80x9d usually suggests and implies xe2x80x9ctibio-talo-calcanealxe2x80x9d arthrodesis. However, in many patients with severe ankle problems, the talus is extensively degraded, and the posterior portion (on which the tibial weight rests, when a person is standing or walking) may be entirely missing, or shrunken to a point where it is not penetrated by a vertical rod. Indeed, a patient with a complete and intact talus rarely offers a good candidate for tibio-calcaneal arthrodesis. Nevertheless, some patients with talus bones that would be penetrated by a vertical rod may be helped by the invention disclosed herein, as can be determined on a case-by-case basis by a skilled surgeon. Accordingly, the term xe2x80x9ctibio-calcanealxe2x80x9d arthrodesis is used herein, regardless of the presence or condition of the talus bone in any specific patient, and regardless of whether the vertical rod component will or will not pass through a talus bone in any specific patient.
The second point of terminology involves the phrase, xe2x80x9ctarsal arthrodesisxe2x80x9d. As is well-known to physicians, the bones in an ankle and foot are divided into three major regions, referred to as the tarsal region (which includes the talus and calcaneal bones, as well as the navicular, cuboid, and certain other bones), the metatarsal region (which includes five relatively long and essentially parallel bones that form the hidden bases of the five toes), and the phalanges (which includes the bones in the toes). Accordingly, a surgical operation that affixes one or more bones in the tarsal portion of the foot can be referred to as tarsal arthrodesis.
All of the rod-and-pin structures that have been developed for ankle arthrodesis over the past 20 years suffer from various limitations. In particular, some patients who have had the device of the prior art inserted into their ankles have suffered from problems involving relative motion between the supposedly affixed tibial and calcaneal bones. This can lead to substantial pain in the affixed joint, and to instability when the patient is walking or standing. It can also lead to additional damage inside the joint, as the screws or other components rub and grind against one or more bones, which are often weakened and relatively soft in patients with severe joint or bone problems.
Accordingly, one object of this invention is to provide an improved type of ankle arthrodesis assembly, which provides better and more stable and reliable fixation of the ankle and hindfoot in patients who need such treatment due to injury or disease of the foot or ankle.
Another object of this invention is to disclose an improved type of ankle arthrodesis assembly for ankle fixation, having a vertical rod which will be inserted vertically through the calcaneal bone and into the lower end of the tibial bone, and an xe2x80x9coblique screwxe2x80x9d which will be inserted at a slanted angle, extending upwardly through the calcaneal bone so that a threaded tip enters the lower end of the tibia.
Another object of this invention is to disclose an improved type of ankle arthrodesis assembly for ankle fixation, having an xe2x80x9coblique screwxe2x80x9d with a threaded tip that will pass through a smooth slanted hole in a vertical rod and enter the lower end of the tibia bone, thereby allowing the threaded screw to exert compression of the tibia against the calcaneum when the screw is tightened.
Another object of this invention is to disclose that when a surgical implant having rod and screw components, positioned at an acute angle with respect to each other, is properly implanted into an ankle that requires arthrodesis, the acute-angled structure provides greater stability and better performance following surgical implantation.
These and other objects of the invention will become more apparent through the following summary, drawings, and description of the preferred embodiments.
A surgical rod-and-screw kit is disclosed, for use in ankle arthrodesis in patients who suffer from severe bone defects in their ankles. This assembly has a vertical intramedullary rod that is inserted through the bottom of the calcaneum (i.e., the heel bone), and driven upward into the tibia (the shin bone). The assembly also has a threaded pin, referred to herein as an oblique screw, which is positioned at an acute angle with respect to the vertical rod. This oblique screw is inserted through the lower rear surface of the calcaneum, and passes through a slanted hole in the vertical rod. The screw has external threads in the tip region, and this threaded tip enters the lower end of the tibial bone. When this screw is tightened, it compresses the-lower end of the tibia bone against the talus and/or calcaneum, which improves the stability of the ankle fixation. This rod-and-screw assembly also reduces the risk and extent of bone damage that can be caused by motion of either or both components during years of use inside a damaged ankle with softened bones. An alignment jig is used during surgery, to help the surgeon align the holes that must be drilled through hard bone for the oblique screw and for fixation screws.